In principle, optical waveguides comprise a thin film or layer of material supported on a substrate of lower refractive index. A ray of light may be propagated within the thin film of higher refractive index material. The ray is confined by total internal reflection at the thin film/substrate interface and at the film/air space boundary. Waveguides are also used for roles additional to merely guiding light. For example, by combining the waveguide with a non-linear element, structures can be produced which are useful in optical logic and signal processing application.
Traditionally, waveguides have been constructed from inorganic materials such as glasses which may be doped with inorganic materials, such as metal or semi-conductor compounds. In order to produce a device which combines waveguiding and non-linear optical properties, it has generally been the practice to grow a single crystal layer onto a suitable base substrate. Such techniques are laborious and complex.
In contrast, the use of organic materials for waveguide construction has been considered to suffer from disadvantages such as lack of stability, insufficient purity, poor optical properties and the difficulty of controlling the incorporation of dopant materials.